1. Field of the Invention
The present invention relates to an ejector cycle.
2. Description of Related Art
As is known in the art, an ejector cycle is one type of vapor compression refrigeration system, in which refrigerant is depressurized and is expanded through a nozzle arrangement of an ejector. High speed refrigerant discharged from the nozzle arrangement exerts drawing force to draw vapor phase refrigerant, which is evaporated in an evaporator, and expansion energy of the refrigerant is converted into pressure energy to increase the intake pressure of a compressor.
In another type of vapor compression refrigeration system, which isentropically depressurizes the refrigerant through a depressurizing means, such as an expansion valve, the refrigerant discharged from the expansion valve is supplied to the evaporator (hereinafter, this vapor compression refrigeration system will be referred to as an expansion valve cycle). Contrary to this, in the ejector cycle, the refrigerant discharged from the ejector is supplied to a gas-liquid separator, and the liquid phase refrigerant, which is separated by the gas-liquid separator, is supplied to the evaporator, and the vapor phase refrigerant, which is separated by the gas-liquid separator, is supplied to the compressor.
That is, in the expansion valve cycle, the refrigerant is circulated through the compressor, the radiator, the expansion valve and the evaporator in this order and is returned to the compressor to form a single refrigerant flow. On the other hand, in the ejector cycle, refrigerant is circulated through the compressor, the radiator, the ejector and the gas-liquid separator in this order and is returned to the compressor to form one refrigerant flow (hereinafter, referred to as a drive flow), and refrigerant is also circulated through the gas-liquid separator, the evaporator and the ejector in this order and is returned to the gas-liquid separator to form another refrigerant flow (hereinafter, referred to as a drawn flow or driven flow). Furthermore, although the drive flow is directly circulated by the compressor, the driven flow is circulated by pumping action of the ejector (see JIS Z8126 Number 2.1.2.3), which uses energy of the high pressure refrigerant compressed by the compressor.
Thus, when the pumping performance or pumping capacity of the ejector is reduced, the flow rate of the driven flow is reduced to cause stagnation of refrigeration oil, which is mixed in the refrigerant, in the evaporator. The stagnation of refrigeration oil in the evaporator, in turn, causes a reduction in heat absorbing capacity of the evaporator and also causes insufficient lubrication of the compressor due to the shortage of refrigeration oil returned to the compressor.
The refrigeration oil is lubricant, which lubricates sliding components of the compressor. In a typical vapor compression refrigeration system, lubrication of sliding components of the compressor is achieved by mixing refrigeration oil into the refrigerant.
Thus, in the ejector cycle, when a degree of throttle opening of the nozzle arrangement of the ejector is controlled to maximize a coefficient of performance with respect to the refrigerant temperature at the radiator outlet in a manner similar to that of a control operation for controlling a degree of throttle opening of the expansion valve of the expansion valve cycle disclosed in, for example, Japanese Unexamined Patent Publication No. 10-89785, which corresponds to U.S. Pat. No. 6,044,655, the following thing happens. That is, when the heat load becomes relatively small, and thus the amount (flow rate) of circulated refrigerant becomes relatively small, the drive flow becomes relatively small. When the drive flow becomes relatively small, the pump capacity of the ejector becomes relatively small. Thus, in the ejector cycle, when the heat load becomes relatively small, there is a higher possibility of stagnation of refrigeration oil in the evaporator in comparison to the expansion valve cycle.